|ORIGINAL ARTICLE - CLINICS IN RENOVASCULAR RADIOLOGY
|Year : 2018 | Volume
| Issue : 4 | Page : 233-239
Renal vasculature: Spectrum of anatomical variations and the significance from a surgeon's standpoint
Swarna1, Yatish Agarwal1, Shalabh Jain1, Avneet Singh Chawla2
1 Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
2 Department of General Surgery, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
|Date of Web Publication||29-Oct-2018|
Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi
Source of Support: None, Conflict of Interest: None
Background: Renal vasculature is known for having a broad spectrum of variants, and some of them hold important implications at the time of renal surgeries, particularly for the renal transplant. Materials and Methods: This observational study was performed using multidetector computed tomography (MDCT) angiography in patients with various renal and other abdominal disorders and advised for pathologies in which MDCT angiography was indicated. A total of 760 patients were evaluated. Various parameters that have surgical importance were studied. Results: This study includes 123 (16%) patients that had accessory renal artery on right side and 152 (20%) patients that had on the left side. Among the right-side renal artery patients, 72 (58.5%) were hilar and 51 (41.5%) were polar arteries, and of left-side patients, 94 (61.8%) were hilar and 58 (38.2%) were polar arteries. The average diameter of the right and left renal artery was 5.1 and 5.07 mm, respectively. The average diameter of the right and left accessory renal artery was 2.4 and 2.6 mm, respectively. Early segmentary bifurcation of the right renal artery was seen in 651 patients (85.6%) with 319 (42%) being retro-caval, and early segmentary bifurcation of the left renal artery was seen in 94 patients (12.3%). Double right and left renal veins were seen in 96 (12.6%) and 37 (4.8%) patients, respectively. Late right renal vein confluence was seen in 50.6% of patients (340/671). Late left renal vein confluence was seen in 181 out of 700 patients (25.85%); 60 (7.9%) patients had circum-/retro-aortic renal vein. Conclusion: CT angiography is highly accurate modality for evaluation of renal vasculature. Although the increasing number of laparoscopic nephrectomies being performed as part of renal transplant procedure, it is becoming important for the radiologists to better understand the anatomy, its variations, its implications, and to accurately demonstrate vascular anatomy on imaging to the surgical team.
Keywords: Renal artery, renal vein, renal transplant
|How to cite this article:|
Swarna, Agarwal Y, Jain S, Chawla AS. Renal vasculature: Spectrum of anatomical variations and the significance from a surgeon's standpoint. Astrocyte 2018;4:233-9
|How to cite this URL:|
Swarna, Agarwal Y, Jain S, Chawla AS. Renal vasculature: Spectrum of anatomical variations and the significance from a surgeon's standpoint. Astrocyte [serial online] 2018 [cited 2019 Mar 19];4:233-9. Available from: http://www.astrocyte.in/text.asp?2018/4/4/233/244294
| Introduction|| |
Many variations are known to exist in the renal arterial and venous anatomy. The importance of these variations lies in surgical planning, particularly in renal transplant donors to avoid adverse surgical outcomes. Living renal donation is being increasingly used for organ procurement to meet the ever-increasing demand. Preoperative roadmap of the renal vasculature helps in meticulous preoperative planning as the field of view at laparoscopic surgery is limited. The major factors that need to be taken into consideration include the origin, number, division, and course of arteries and veins. The best noninvasive preoperative planning method for anatomic evaluation is multidetector computed tomography (MDCT) angiography, which helps in defining different variations in a living patient preoperatively and better planning of the surgical procedure. Knowledge of these patterns has gained significance in providing information to the surgeon in order to avoid compromising the safety of surgical procedure that could lead to significant complications. The purpose of this study was to study the anatomic variations in the origin and course of renal arteries and veins using MDCT angiography and be aware of the variations that need special attention or possibly a contraindication for a particular procedure.
| Materials and Methods|| |
This observational study was approved by the Ethical Board of the institution. MDCT abdominal angiography scans were performed on patients sent for various renal and other abdominal pathologies in which contrast-enhanced CT angiography was indicated. Patients with a history of major abdominal surgery were excluded from the study. A total of 760 patients were evaluated. The study population comprised 397 men and 363 women (mean age of 41.2 years).
CT examination protocol
MDCT angiography was performed on Philips Brilliance 40-slice scanner after injecting maximum of 120 mL of nonionic iodinated contrast material (iodine concentration, 370 mg/mL) through an 18–20-gauge antecubital intravenous cannula at a rate of 5–6 mL/s using bolus tracking technique. The arterial phase was obtained from dome of diaphragm to mid-sacrum.
The data obtained from MDCT angiography were evaluated on a dedicated three-dimensional (3D) workstation. The following reconstructions were obtained for all the cases: axial thin-section maximum intensity projection (MIP) images of the renal arteries and veins, curved coronal reformation of renal arteries and veins using MIP, and 3D volume-rendered images. These images were analyzed independently by three radiologists: Radiologist 1 (S.) with 7 years, Radiologist 2 (S.J.) with 7 years, and Radiologist 3 (Y.A.) with 24 years of experience in interpreting CT scans. The renal vasculature anatomy was analyzed and certain surgically important parameters were considered. The parameters studied included number of renal arteries on either side, orthogonal diameter of bilateral main as well as accessory renal arteries, origin of accessory renal arteries if any, distance of accessory renal artery from main renal artery and classification of accessory arteries as hilar/polar, distance of segmentary bifurcation of the right main renal artery from origin and from right margin of inferior vena cava (IVC), distance of segmentary bifurcation of the left main renal artery from origin, number of renal veins on either side, distance of confluence of the right renal vein to IVC, and distance of confluence of the left renal vein to IVC and from aorta.
We used some key definitions described by various authors for evaluating the arteries as follows:
- The accessory arteries: When a kidney has two or more arteries with a separate ostium, the vessel with the greatest diameter is considered to be the main renal artery and the others as accessory arteries
- Hilar/polar renal artery: hilar, entering at the hilium, and polar, reaching at the pole
- Early segmentary bifurcation of the right renal artery: within 1 cm of right margin of IVC
- Early segmentary bifurcation of the left renal artery: within 15 mm
- Late right renal vein confluence: <15 mm from IVC
- Late left renal vein confluence: <15 mm from left aortic margin
| Results|| |
Number of renal arteries: A total of 760 subjects were analyzed. Out of 760 patients, 123 (16%) patients had accessory renal artery on the right side and 152 (20%) patients had accessory artery on the left side. There were 51 (6.7%) patients who had simultaneous bilateral accessory renal arteries. All the accessory renal arteries in our study were seen to arise from the abdominal aorta.
Out of 123 right accessory renal arteries, 72 (58.5%) were hilar and 51 (41.5%) were polar arteries.
Out of 152 left accessory renal arteries, 94 (61.8%) were hilar and 58 (38.2%) were polar arteries.
Main renal artery diameters: Out of the 1520 main renal arteries (760 right and 760 left) studied, 11 main renal arteries (0.7%) had diameter <3 mm and all of them were on the left side. An average diameter of the right renal artery was 5.1 mm with a maximum diameter of 8 mm and minimum of 3.1 mm. The average diameter of left renal artery was 5.07 mm with a maximum diameter of 8.4 mm and minimum of 2.9 mm.
Right accessory renal artery diameter: The minimum diameter was 1.9 mm with maximum diameter of 3.4 mm and average diameter of 2.4 mm.
Left accessory renal artery diameter: The minimum diameter was 1.8 mm with maximum diameter of 4 mm and average diameter of 2.6 mm.
Early segmentary bifurcation of the right renal artery: This was seen in 651 patients (85.6%) with 319 (42%) being retro-caval.
Early segmentary bifurcation of the left renal artery: This was seen in 94 patients (12.3%). Mean length of bifurcation was 25.03 mm with maximum of 44.5 mm and minimum of 1.1 mm.
Double right renal veins: Double right renal veins were seen in 96 (12.6%) patients.
Late right renal vein confluence: Late right renal vein confluence was seen in 50.6% of patients (340/671). An average distance of the right renal vein confluence was 4.88 mm with a maximum of 34 mm and minimum of 2 mm.
Double left renal veins: These veins were seen in 37 patients (4.8%): 21 (2.7%) of the double renal veins drain into gonadal veins and rest 16 (2.1%) into IVC directly.
Late left renal vein confluence: This was seen in 181 out of 700 patients (25.85%); 60 (7.9%) patients had circum-/retro-aortic renal vein. The average distance of left renal vein confluence from aorta is 22.49 mm with a maximum of 41.3 mm and minimum of 3.5 mm.
The distance between right main renal artery and accessory renal artery: The minimum distance was 0 mm, and both the arteries arise from the same level. The maximum distance was 38 mm below the main renal artery with an average distance of 8.3 mm. Out of 123 accessory renal arteries, 9 (7.3%) were seen to arise above the main renal artery, 21 (17%) were seen to arise at the same level, and rest 93 arteries (75.7%) arose below the level of main renal arteries.
The distance between left main renal artery and accessory renal artery: The minimum distance was 0 mm; that is, both the arteries arise from the same level. The maximum distance was 53 mm below the main renal artery with an average distance of 9.6 mm. Out of 152 accessory renal arteries, 82 (53.9%) were seen to arise above the main renal artery, 12 (7.9%) were seen to arise at the same level, and rest 58 arteries (38.2%) arose below the level of main renal arteries.
| Discussion|| |
The gold standard imaging technique for evaluation of renal vessels is conventional angiography. However, MDCT angiography is increasingly being used as an initial choice of technique for demonstration of the renal vascular anatomy as it is less invasive and easily available.,, MDCT angiography enables precise visualization of the normal and variant anatomy of the renal vasculature,,, which has its relevance in preparing the vascular roadmap before any surgical intervention [Figure 1] and [Figure 2], especially in choosing the donors for renal transplant. MDCT has an accuracy of 95–100% with the use of a 4–8, 16, or 64-row scanner.,,
|Figure 1: Volume-Rendered Image of Renal Arteries Arising from Aorta with Normal Arterial Segmentary Bifurcation.|
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Systematic analysis of CT angiography images was performed and we were able to identify and quantify various parameters which have important implications and are relevant for surgical planning.
In our study of 760 patients, 123 (16%) patients had accessory renal artery on the right side, 152 (20%) patients had accessory artery on the left side [Figure 3], and 51 (6.7%) patients had simultaneous bilateral accessory renal arteries [Figure 4]. Out of 123 right accessory renal arteries, 72 (58.5%) were hilar and 51 (41.5%) were polar arteries. Out of 152 left accessory renal arteries, 94 (61.8%) were hilar [Figure 5] and 58 (38.2%) were polar arteries [Figure 6]. According to the study by Uflacker, 24% kidneys have two renal arteries; of those with two arteries, 12% contain two hilar arteries, 12% contain one hilar and one polar artery. Other studies also report prevalence of accessory arteries in the range of 23–32%.,, Bilateral multiple renal arteries occur in 15%. It is important to report the number of renal arteries as the surgeons prefer kidneys with single artery in case of renal transplant as both donor and recipient surgeries are less complicated and there is less risk for arterial thrombosis. It is also important to mention the origin of the accessory artery as there is limited field of view at the time of laparoscopic surgery. Moreover, the use of kidneys with inferior accessory polar artery for the purpose of renal donation is avoided because of the risk of pyelo-ureteral damage if they are cut or thrombosed, thus resulting in stricture formation or urinary leak. When a kidney has two arteries, the length of the arteries before the segmentary bifurcation and the distance between the two arteries must be measured, and 3D volume-rendered images should be obtained. The surgeon evaluates these images and determines if side-to-side or end-to-side anastomosis of the arteries is possible. If end-to-side or side-to-side anastomosis is not possible, then double arterial anastomosis is performed in the iliac artery of the recipient kidney.
|Figure 3: MIP Coronal Image Reveals Two Renal Arteries on the Left Side. The Artery with Narrow Caliber is Named as Accessory Artery, Which is the Cranial One in This Case. The Artery with Wider Caliber is Taken as Main Renal Artery.|
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|Figure 4: MIP Coronal Images Reveal Simultaneous Bilateral Accessory Renal Arteries.|
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|Figure 5: Volume-Rendered Image Shows Two Renal Arteries on the Right Side with Hilar Accessory Renal Artery Entering the Renal Hilum.|
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|Figure 6: MIP Axial Images Reveal Left Renal Accessory Artery Supplying the Lower Pole of Kidney.|
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Out of the 1520 main renal arteries (760 right and 760 left) studied, 11 main renal arteries (0.7%) had diameter <3 mm and all of them were on the left side. The average diameter of right renal artery was 5.1 mm, with a maximum diameter of 8 mm and minimum of 3.1 mm. The average diameter of left renal artery was 5.07 mm, with a maximum diameter of 8.4 mm and minimum of 2.9 mm. For the right-side accessory renal arteries, the minimum diameter was 1.9 mm with a maximum of 3.4 mm and average diameter of 2.4 mm, and on the left side, the minimum diameter was 1.8 mm with a maximum of 4 mm and average diameter of 2.6 mm. It is necessary to measure the real orthogonal diameter of all the renal arteries for safe recipient arterial graft anastomosis, and arterial orthogonal diameter must be at least 3 mm. In arteries <3 mm, there are high chances of thrombosis. Small vessels measuring <2 mm can be sacrificed in case of renal donors as they are likely to produce graft infarct volume of <10%.
Early segmentary bifurcation of the right renal artery was seen in 651 patients (85.6%), with 319 (42%) being retro-caval [Figure 7]. Early segmentary bifurcation of the left renal artery [Figure 8] was seen in 94 patients (12.3%), with mean length of bifurcation of 25.03 mm, maximum of 44.5 mm, and minimum of 1.1 mm. According to earlier studies, early segmentary bifurcation is seen in 10–12% cases. According to Raman et al., early branching of the left renal arteries (<2 cm from the aorta) is present in 21% of cases, whereas early branching of the right renal arteries is present in 15% of individuals. It is important to detect any early segmentary bifurcation, to ensure adequate control and vascular anastomosis at the time of surgery. In case of retro-caval bifurcation, there is a high possibility of injuring IVC.
|Figure 7: MIP Axial Images Show Segmentary Bifurcation of the Right Renal Artery Behind the IVC Suggestive of Retro-Caval Bifurcation.|
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|Figure 8: Volume-Rendered Image of Renal Vasculature Reveals Early Bifurcation of the Left Renal Artery with Bifurcation Just After Origin.|
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Double renal veins [Figure 9] were seen in 96 (12.6%) and 37 (4.8%) patients on the right and left side, respectively. Late right renal vein confluence was seen in 50% of patients (340/671) with average distance being 4.88 mm, maximum of 34 mm, and minimum of 2 mm: 21 (2.7%) of the double left renal veins were seen draining into gonadal veins and rest 16 (2.1%) into IVC directly. Late left renal vein confluence [Figure 10] was seen in 181 out of 700 patients (25.85%); and 60 (7.9%) patients had circum-aortic [Figure 11]a and [Figure 11]b/retro-aortic renal vein [Figure 12]a and [Figure 12]b. The average distance of left renal vein confluence from aorta is 22.49 mm, with a maximum of 41.3 mm and minimum of 3.5 mm. According to earlier studies, double renal veins are usually seen in the right kidney and their prevalence varied from 8 to 15% of cases., The circum-aortic and retro-aortic veins (present in 9%) are the most common major venous variants in the left kidney and are related to the embryologic development of the IVC.,,,,
|Figure 9: MIP Coronal Images Reveal Dual Renal Veins on the Right Side as Pointed by Arrows. The Two Veins are Seen to Drain into IVC Separately.|
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|Figure 10: MIP Coronal Images Reveal Late Confluence of the Left Renal Vein. The Arrows Point Two Separate Segmentary Veins.|
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|Figure 11: (a) MIP Axial Image Reveals Circum-Aortic Vein Seen as Two Separate Venous Channels Anterior as Well as Posterior to the Aorta Draining from Left Kidney into IVC. (b) MIP Sagittal Images Show the Circum-Aortic Vein in the Same Patient. Two Separate Venous Structures can be Seen Anterior as Well as Posterior to the Aorta as Marked with Arrows.|
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|Figure 12: (a) MIP Axial Image Reveals Retro-Aortic Left Renal Vein. Single-Venous Structure Draining from the left Kidney is Seen Coursing Posterior to Aorta Draining into IVC. No Venous Structure is Seen Anterior to Aorta as in the Case of Circum-Aortic Vein. (b) MIP Sagittal Image Reveals Retro-Aortic Vein as Marked by Arrow.|
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The present study had some limitations. First, fine arterial or venous networks could have been missed and was beyond the capability of CT examination; however, the knowledge on these vascular channels are not much of clinical importance. Second, the various definitions used for describing the variations are not standard for every institution and surgeon as they largely depend on the surgical expertise available. This study is the first of its kind that comprehensively describes variations in renal vasculature in Indian population. Importance of knowing these variations and accurate radiological reporting cannot be underestimated in order to avoid life-threatening complications.
Preoperative CT evaluation of prospective renal donors using MDCT angiography not only helps in depicting the presence or absence of renal arterial and venous variants but also helps in detecting abnormalities of the renal parenchyma and collecting system, renal calculi, and other renal and extrarenal abnormalities that help in further planning.
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Conflicts of interest
There are no conflicts of interest.
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